This invention relates generally to arrays of extremely small solid-state lasers and, more particularly, to techniques for producing higher peak powers in arrays of solid-state lasers. There are a number of useful applications for arrays of lasers of moderate to high peak powers, such as in printing applications.
A conventional technique, referred to as Q switching, is often used to obtain higher peak powers from lasers. As is well known, light in a laser cavity makes repeated reflections from opposed mirrors that define one dimension of the cavity. The Q factor, or quality factor, of a laser cavity can be considered to be a measure of the number of round trips taken by light in the cavity before being outcoupled as emitted light. A Q switch is simply a device for varying the Q of a cavity, usually by selecting a high or a low value. A zero Q value means that lasing is suppressed almost completely, while a high Q means that lasing is taking place in the cavity. A simple form of Q switch is a mechanical shutter disposed in the laser cavity. If the shutter is closed, the Q of the cavity is zero. Laser action cannot then occur but energy is effectively stored in the cavity for some types of lasers. If the shutter is then suddenly opened, switching to a higher Q, the stored energy will be released in the form a short and intense light pulse. Other types of Q switches use electro-optical shutters, or piezoelectric transducers to move the cavity mirrors.
Although Q switching is a well known technique, most Q switches tend to be extremely bulky and to have a relatively long switching time. Consequently, Q switches are harder to develop for extremely small lasers, or microlasers, and it is difficult to scale traditional Q switch designs down to the sizes needed in microlaser arrays. Moreover, as the laser cavities under consideration get smaller and smaller, energy builds up faster than for larger cavities and the Q switch must be correspondingly faster in operation.
Electro-absorptive switches have been used as light modulators external to laser cavities. In U.S. Pat. No. 5,151,915 to Paoli, an electro-absorptive element is disclosed for use in a semiconductor diode array. Application of appropriate bias voltages to the electro-absorptive elements is used to selectively switch the diodes in the array on or off, but no energy is stored in the cavities of those in the off condition because semiconductor diode lasers are incapable of storing energy when not lasing.
It will be appreciated from the foregoing that there is a need for a highly compact laser array structure having laser elements that are individually addressable to produce moderate to high peak output powers. The present invention meets this need, as will become apparent from the following summary.